Ldmos power semiconductor device and manufacturing method of the same

ABSTRACT

An electronic semiconductor device comprising: a semiconductor body, having a first side and a second side opposite to one another and including a first structural region facing the second side, and a second structural region extending over the first structural region and facing the first side; a body region extending in the second structural region at the first side; a source region extending inside the body region; an LDD region facing the first side of the semiconductor body; and a gate electrode. The device comprises: a trench dielectric region extending through the second structural region a first trench conductive region immediately adjacent to the trench dielectric region; and a second trench conductive region in electrical contact with the body region and with the source region. An electrical contact at the second side of the semiconductor body is in electrical contact with the drain region via the first structural region.

BACKGROUND

1. Technical Field

The present disclosure relates to an LDMOS semiconductor device and to amethod for manufacture thereof.

2. Description of the Related Art

As is known, some applications of MOSFET power devices (or powerMOSFETs) operate said MOSFET power devices at high switchingfrequencies. An example is that of electrical switches used in the fieldof high-frequency pulse-width modulation (PWM). In order to maximize theefficiency of the device, it is expedient for the levels of dynamicperformance to exhibit a negligible loss of power during the switchingoperations. Said condition is obtained by minimizing the values ofcapacitance of the parasitic capacitors internal to said devices.Particular attention is directed at minimization of the gate-to-draincapacitance C_(GD), since said capacitance C_(GD) determines theduration of the period of transient of the voltage signal duringswitching. It is hence of importance to minimize the value ofcapacitance C_(GD) so as to minimize the power losses of the MOSFETpower device. A parameter, which is strictly linked to the parasiticcapacitance and is typically used for characterizing the efficiency of aMOSFET power device during switching, is the gate charge Q_(G). In fact,the value of gate charge Q_(G) furnishes an estimate of the amount ofcurrent to supply to the gate terminal of the MOSFET power device toobtain switching of said device from the off state (in which it does notconduct electric current) to the on state (in which there is conductionof electric current between the source and drain terminals).

Lateral double-diffused MOSFETs (LDMOSs) can advantageously be used in awide range of frequencies, with powers that range from a few watts to afew hundred watts. A classic LDMOS structure comprises a substrate,which has, in lateral sectional view, a horizontal sequence constitutedby a low-resistance laterally diffused area (of a P+ type, referred toas “sinker”), a source region, a gate region, and a light-doped-drain(LDD) region that provides the drain terminal. The LDD region moreoverfaces a surface of the substrate. Said structure of a known type forms,for obvious reasons, an elementary cell with a large pitch.

Lateral MOSs have been amply studied, and known in the literature aretechniques of minimization of the internal capacitances and informationon how to obtain values of drain-to-source on-state resistance (R_(DS)_(—) _(ON)) that are comparable with the values of the technology oftrench field-effect transistors (also known as “trench-FETs”).

FIG. 1 shows an LDMOS transistor of a known type, in particulardescribed in U.S. Pat. No. 7,936,007. With reference to FIG. 1,represented therein is a lateral sectional view of a structure designedto minimize the pitch of the base cell of an LDMOS. In this case, anLDMOS transistor 1 includes a substrate 2, having a top surface 2 a anda bottom surface 2 b opposite to one another, in which an LDD region 3extends from the top surface 2 a of the substrate 2 to the bottomsurface 2 b (without actually reaching the bottom surface 2 b). In anarea corresponding to the bottom surface 2 b a drain region 4 ispresent. The LDD region 3 is obtained by forming, starting from the topsurface 2 a of the substrate 2, implanted regions 5 a and 5 b, of an Ntype, self-aligned to the gate terminal 6 and interposed between twogate terminals 6 set alongside one another. A sinker region 7 extends inthe substrate 2, in areas corresponding to body regions 10, underneathsource regions 9. A conductive layer 8 extends above, and electricallyinsulated from, the gate terminal 6, and penetrates into the substrate 2until it contacts the source region 9 and the sinker region 7.

In order to minimize the parasitic capacitance between the gate terminal6 and the LDD region 3, the structure shown in FIG. 1 may be modified insuch a way that the conductive layer 8 extends over the side wall 6 a ofthe gate terminal 6, above the LDD region 3. By connecting theconductive layer 8 to a ground reference terminal, a conductive “shield”is formed, designed to attenuate the phenomenon known as “hot-carrierinjection” (HCl) and improve gate/drain decoupling. In addition, it isexpedient to envisage a dielectric layer 11 in order to separate theportion of the conductive layer 8 that extends above the LDD region 3from the top surface 2 a of the substrate 2. Said dielectric layer 11 ofseparation preferably has a thickness in the region of 100-200 nm. Asolution in this direction is the one described in U.S. Pat. No.7,589,378 (not shown in the figure). In this case, an LDMOS transistorwith LDD surface region is proposed in which a conductive shield extendsover the gate terminal and alongside it, above the LDD region, andseparated from the latter by means of a dielectric layer. In this way, areduction of the electrical field is obtained with consequent benefit interms of increase of the on-state drain-to-source resistance R_(DS) _(—)_(ON) and attenuation of the value of gate-to-drain capacitance. Asmentioned previously, the solution with LDD surface region imposesconstraints on the minimum pitch that can be obtained, which can bereduced further only at the expense of the value of breakdown voltage,which drops considerably.

As an alternative, more complex processes may be used, of the typedescribed in U.S. Pat. No. 7,829,947, wherein a power LDMOS has afield-oxide region underneath the gate region in order to minimize thecapacitance between the gate region and the LDD region. Said device,however, presents major manufacturing difficulties in order to controloverlapping between the LDD region and the gate region.

BRIEF SUMMARY

Some embodiments of the present disclosure provide an LDMOSsemiconductor device and a method for manufacture thereof that will befree from the drawbacks of the known art.

According to one embodiment of the present disclosure an LDMOSsemiconductor device includes:

a semiconductor body having a first side and a second side opposite toone another along a first direction and including a first structuralregion, which faces the second side and has a first conductivity; and asecond structural region which extends over the first structural region,faces the first side, and has a second conductivity opposite to thefirst conductivity;

a body region having the second conductivity and extending in the secondstructural region at the first side;

a source region having the first conductivity, extending within the bodyregion and facing the first side;

a drain region having the first conductivity and facing the first sideof the semiconductor body;

a gate electrode extending over a portion of the first side of thesemiconductor body between the source region and the drain region;

a first trench which extends through the second structural region andhouses a trench dielectric region and a first trench conductive region;and

a second trench which extends through part of the second structuralregion inside the body region, said second trench housing a secondtrench conductive region electrically connected with the body region andwith the source region.

The drain region extends through the second structural region,electrically contacts the first structural region, and is arrangedbetween, and in direct contact with, the body region and the trenchdielectric region, said first and second trench conductive regions beingelectrically coupled to one another.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

For a better understanding of the present disclosure, preferredembodiments thereof are now described, purely by way of non-limitingexample, with reference to the attached drawings, wherein:

FIG. 1 illustrates, in lateral sectional view, a MOSFET device accordingto an embodiment of a known type;

FIG. 2 shows, in lateral sectional view, an elementary cell of a powerdevice according to one embodiment of the present disclosure;

FIG. 3 shows an enlarged detail of the cross section of the power deviceof FIG. 2;

FIG. 4 shows, in lateral sectional view, an elementary cell of a powerdevice according to a further embodiment of the present disclosure;

FIG. 5 shows, in lateral sectional view, an elementary cell of a powerdevice according to a further embodiment of the present disclosure;

FIG. 6 shows, in lateral sectional view, an elementary cell of a powerdevice according to a further embodiment of the present disclosure;

FIG. 7 shows, in lateral sectional view, an elementary cell of a powerdevice according to a further embodiment of the present disclosure;

FIG. 8 shows, in lateral sectional view, an elementary cell of a powerdevice according to a further embodiment of the present disclosure;

FIGS. 9-24 show, in lateral sectional views, steps for manufacturing apower device comprising two elementary cells of the type shown in FIG.2;

FIG. 25 shows, in lateral sectional view, an elementary cell of a powerdevice according to a further embodiment of the present disclosure;

FIG. 26 shows, in lateral sectional view, an elementary cell of a powerdevice according to a further embodiment of the present disclosure;

FIGS. 27 a-27 e show a detail of embodiment of a portion of theelementary cell of FIG. 26;

FIG. 28 a shows a circuit diagram of a half-bridge block including twotransistors coupled together through a common terminal;

FIG. 28 b shows, in lateral sectional view, an embodiment of thehalf-bridge block of FIG. 28 a, in which one of the transistors isprovided according to any one of the embodiments of FIG. 2, 4-8 or 26;

FIG. 29 shows, in lateral sectional view, an elementary cell of a powerdevice according to a further embodiment of the present disclosure; and

FIG. 30 shows, in lateral sectional view, an elementary cell of a powerdevice according to a further embodiment of the present disclosure.

DETAILED DESCRIPTION

According to the present disclosure, a power device is provided, inparticular a lateral-diffusion MOS transistor (LDMOS) with drainelectrode on the back of the device.

FIG. 2 is a schematic view, in lateral section, of a portion of a powerdevice 20. The view of FIG. 2 represents an elementary cell 21 of thepower device 20. The latter may comprise just one elementary cell 21 ora plurality of elementary cells of the type shown in FIG. 2. Theelementary cell 21 extends from the segment A to the segment B, and theportion comprised between A and B may be ideally replicated and thenreflected specularly with respect to the segment A and/or to the segmentB to obtain a power device 20 comprising a plurality of elementary cells21.

The elementary cell 21 of FIG. 2 comprises a substrate 22, made ofsemiconductor material such as, for example, silicon having a firstconductivity (e.g., of an N+ type). The substrate 22 is delimited by afirst side 22 a and by a second side 22 b opposite to one another in adirection Z.

Extending over the substrate 22 is a structural region 26, for examplemade of silicon grown epitaxially, having a second conductivity (e.g.,of a P− type), different from the first conductivity. The structuralregion 26 has a thickness chosen according to the need, in particularapproximately 1.2 μm or 1.3 μm. It is evident that other values may bechosen, for example any value of thickness starting from 0.6 μm.

According to other embodiments, the structural region 26 has the firstconductivity (e.g., of an N− type) and a value of conductivity lowerthan the value of conductivity of the substrate 22.

The structural region 26 is delimited by a first side 26 a and by asecond side 26 b opposite to one another in the direction Z. The secondside 26 b of the structural region 26 faces the first side 22 a of thesubstrate 22. According to one embodiment, the second side 26 b of thestructural region 26 is in direct electrical contact with the first side22 a of the substrate 22. According to alternative embodiments (notshown), one or more further structural regions, for example grownepitaxially and similar to the structural region 26 and/or to the region22, extend between the first side 22 a of the substrate 22 and thesecond side 26 b of the structural region 26.

Extending over the first side 26 a of the structural region 26 is adielectric layer 28, for example made of silicon oxide, having thefunction of gate oxide.

A gate electrode 30 extends over the dielectric layer 28. The gateelectrode 30 is formed by a stack of layers of polysilicon with N+doping 30 a, silicide 30 b, insulating material 30 c (e.g., siliconoxide), and silicon nitride 30 d. According to one embodiment, thesilicide layer 30 b is constituted by a metal layer, obtained byreaction with cobalt, or else via deposition of tungsten silicide insequence to the polysilicon, or in any other way.

A drain region 38, having the first conductivity (of an N type), extendsin the direction Z between the first side 26 a of the structural region26 and the first side 22 a of the substrate 22, substantially alignedwith a side wall 30′ of the gate electrode 30 (or in any caseoverlapping to a minimal extent the gate electrode 30). In top planview, the drain region 38 extends alongside, in the direction X, thegate electrode 30, and possibly overlaps the gate electrode, as aconsequence of the steps of the manufacturing process.

A trench 31 extends in depth in the direction Z, in the structuralregion 26, and in part of the substrate 22, and terminates in thesubstrate 22. A first trench conductive region 32 extends inside thetrench 31 and is surrounded by one or more dielectric layers (in FIG. 2a first trench dielectric 34 and a second trench dielectric 36 areillustrated).

The trench 31 extends alongside (in the direction X) the gate electrode30 and the drain region 38. The first trench conductive region 32 iselectrically insulated from the gate electrode 30 by the second trenchdielectric 36 (and, as described more fully hereinafter by a furtherdielectric designated in the figure by the reference number 40 a). Inaddition, the first trench conductive region 32 is electricallyinsulated from the drain region 38 by the first and second trenchdielectrics 34, 36. Moreover, the first and second trench dielectrics34, 36 insulate electrically the first trench conductive region 32 fromthe substrate 22.

Hence, both the first and the second trench dielectrics 34, 36 aredesigned to insulate electrically the first trench conductive region 32from the structural region 26 and from the substrate 22, whereas thesecond trench dielectric 36 and the dielectric 40 a are designed toinsulate electrically the first trench conductive region 32 from thegate electrode 30.

The first trench conductive region 32 forms an electrode, which can beconnected to a reference voltage GND (e.g., connected to ground)designed to reduce the electrical field, and hence generation of hotelectrons in the drain region 38, in particular in areas correspondingto the portion of the drain region 38 that extends in the proximity ofthe gate electrode 30. This enables a good control (in particular, areduction) of the phenomena of charge trapping or injection (known as“hot-carrier injection”) in the drain region 38. The distance betweenthe first trench conductive region 32 and the drain region 38 may beadjusted by choosing appropriately the thickness of the first and secondtrench dielectrics 34, 36.

The present applicant has found that a thin trench dielectric (forexample in the range of approximately 50-200 nm, extremes included)makes it possible to approach the first trench conductive region 32 tothe drain region 38, with consequent reduction of the electrical field(potential lines) in the portion of the structural region 26 in whichthe drain region 38 faces the gate electrode 30. This leads, as has beensaid, to the advantage that the phenomenon of generation of hotelectrons is minimal even at high doping concentrations of the drainregion 38.

Moreover, this enables an optimal compromise to be achieved betweencontrol of the aforementioned electrical field and the dose of doping ofthe LDD region, which, if increased as compared to the solutions of aknown type, enables reduction of the drain-to-source on-state resistanceR_(DS) _(—) _(ON).

Formation of the drain region 38 will be described more fullyhereinafter, and is obtained place via slanted implantation, where theangle is chosen such a way that the drain region 38 thus formed extendsbetween the first side 26 a and the second side 26 b of the structuralregion 26, substantially adjacent to the first trench dielectric 34, andis in electrical contact with the substrate 22.

At the second side 22 b of the substrate 22 a first metallization 41 ispresent, in electrical contact with the substrate 22. In use, the drainregion 38, the substrate 22, and the first metallization 41 form a drainelectrode of the power device 20.

The elementary cell 21 of FIG. 2 further comprises lateral spacers 40 a,40 b (made of dielectric material), which extend along side walls 30′ ofthe gate electrode 30. In particular, the lateral spacer 40 a extendsbetween the gate electrode 30 and the second trench dielectric 36, abovethe drain region 38 and substantially aligned, in the direction Z, withthe drain region 38. The lateral spacer 40 a has a maximum extension,measured in a direction X orthogonal to the direction Z, comprisedbetween approximately 100 nm and 200 nm. Said maximum extension ispresent at the interface between the lateral spacer 40 a and thedielectric layer 28 on which the lateral spacer 40 a lies. The spacer 40b has a shape similar to that of the spacer 40 a and extends in areascorresponding to the wall 30′ opposite, in the direction X, with respectto the wall 30′ along which the spacer 40 a extends. The spacers 40 aand 40 b are made of dielectric material, for example silicon oxide.

The elementary cell 21 of FIG. 2 further comprises a body region 44,having the second conductivity (of a P type), which extends in thestructural region 26 facing the first side 26 a. In greater detail, thebody region 44 extends in the structural region 26 for a depth in thedirection Z equal, for example, to approximately 0.5 or 0.6 μm;moreover, the body region 44 borders laterally (i.e., in the directionX) on a portion of the drain region 38.

In addition, a source region 46 extends in the body region 44, facingthe first side 26 a of the structural region 26, for a depth in thedirection Z comprised, for example, between approximately 100 nm and 150nm. The source region 46 has the first conductivity (e.g., of an N+type) and overlaps, in top plan view, to the gate electrode 30 by anamount, measured along the axis X, comprised for example betweenapproximately 0.05 μm and 0.15 μm.

In use, the portion of the body region 44 comprised between the sourceregion 46 and the drain region 38 houses the conductive channel of thepower device 20.

An enriched region 48 (p-well), having the second conductivity and avalue of doping higher than that of the body region 44 (e.g., P+, with aconcentration of around 1·10¹⁸ cm⁻³), extends in the body region 44underneath the source region 46 (i.e., substantially vertically alignedto the source region 46 in the direction Z). The enriched region 48 hasthe function of reducing, in use, the sheet resistance of the bodyregion 44, which is located underneath the source region 46, so as toprevent turning-on of a parasitic bipolar transistor in the avalanchemultiplication during breakdown.

The elementary cell 21 of FIG. 2 further comprises a second trench 51,housing a second trench conductive region 52, which extends in the bodyregion 44 through the dielectric layer 28, in an area corresponding tothe source region 46 and the enriched region 48, terminating inside theenriched region 48. The second trench conductive region 52 is hence inelectrical contact with the source region 46 and with the enrichedregion 48. In this way, the source region 46 and the body region 44 areboth electrically coupled to the trench conductive region 52 and, viathe latter, are electrically coupled together.

The second trench conductive region 52 is moreover electricallyseparated from the gate electrode 30 by the spacer 40 b.

A second metallization 56 extends over the first trench conductiveregion 32, the second trench conductive region 52, and the gateelectrode 30, in electrical contact with the first trench conductiveregion 32 and the second trench conductive region 52, and electricallyinsulated from the gate electrode by the silicon-nitride layer 30 d andthe dielectric layer 30 c.

In this way, via the second metallization 56, the body region 44 and thesource region 46 are electrically coupled to the first trench conductiveregion 32.

In use, according to one embodiment of the present disclosure, thesecond metallization 56 is biased at a reference voltage GND (forexample, ground).

The present applicant has found that lowering the parasitic capacitanceC_(GD) between the gate electrode 30 and the drain region 38, moreeffectively decouples the gate electrode 30 electrically from the drainregion 38. According to the embodiment of FIG. 2, the gate electrode 30is electrically decoupled from the drain region 38 via the body region44. According to one aspect of the present disclosure, in use, the bodyregion 44 is biased at the reference voltage GND via the second trenchconductive region 52 and the second metallization 56. The drain region38, as has been said, is of a vertical type and extends in thestructural region 26 along Z; likewise, also the first trench conductiveregion 32 extends vertically along Z in the structural region 26, andborders laterally (along X) on the drain region 38. According to thestructure described, the only contributions at the basis of electricalcoupling between the gate electrode 30 and the drain region 38 are: (i)electrical coupling due to the overlapping portion between the drainregion 38 and the gate electrode 30, through the insulating layer 28;and (ii) electrical coupling due to the interaction between the sidewall 30′ of the gate electrode 30 and the drain region 38.

FIG. 3 shows an enlarged detail of the portion of the elementary cell 21of FIG. 1 that houses the parasitic capacitances C_(P1) and C_(P2) atthe basis of the aforementioned contributions (i) and, respectively,(ii) of the electrical coupling between the gate electrode 30 and thedrain region 38. It should moreover be noted that the surface portion ofthe drain region 38 that interacts with the aforesaid side wall 30′ ofthe gate electrode 30 is the one that extends for a length, along X,equal to that of the base of the spacer 40 a.

Some applications desire threshold voltages of the power device 20ranging between 1 V and 2 V. This entails the use of low concentrationsof P doping of the body region 44 (around 5·10¹⁶-2·10¹⁷ cm⁻³) when thickgate oxides are used (in the region of 40-60 nm; in FIG. 2 the gateoxide is represented by the dielectric layer 28). Instead, when thingate oxides are used (in the region of 30-40 nm), high concentrations ofP doping of the body region 44 are used (around 2·10¹⁷-5·10¹⁷ cm⁻³). Thesolutions with thick gate oxide enable reduction of the contribution ofthe gate-to-drain capacitance C_(GD) due to the overlapping between thedrain region and the gate electrode. At the same time, said solutionsrequire gate dimensions in the region of 0.5 μm-0.6 μm (gate width W,i.e., measured along X between the drain region 38 and the source region46) in order to prevent the “punch-through” phenomenon. Thin gate oxidesenable scaling of the dimensions and can be accompanied by an increaseof dose of doping of the body region 44.

FIG. 4 shows an elementary cell 61 of a power device 60 according to anembodiment alternative to that of FIG. 2. Elements of the elementarycell 61 that are in common to those of the elementary cell 21 of FIG. 2are designated by the same reference numbers and are not described anyfurther.

According to the embodiment of FIG. 4, the first trench conductiveregion 32′ of the elementary cell 61 is similar to the first trenchconductive region 32 of the elementary cell 21 of FIG. 2, but extends inthe structural region 26, in the direction Z, until it reaches a depthsmaller than the thickness, measured along Z starting from the firstside 26 a, of the structural region 26. For example, the first trenchconductive region 32′ of the elementary cell 61 extends to a depth alongZ substantially equal to approximately half of the thickness of thestructural region 26. Extending underneath the first trench conductiveregion 32′, and in contact with the latter, is a filling region 64, madeof a dielectric material or of a number of dielectric materials inlayers set on top of one another, for example silicon nitride and/orsilicon oxide. Both the first trench conductive region 32′ and thefilling region 64 are surrounded by the second trench dielectric 36. Inthis way, the first trench conductive region 32′ of FIG. 4 extends inthe power device 60 until it reaches a maximum depth smaller than themaximum depth reached by the first trench conductive region 32′ of thepower device 20 of FIG. 2. The reduction of the depth reached by thefirst trench conductive region 32′ of the power device 60 (which, as hasbeen said, in use, is biased at a reference voltage GND, typicallyground) attenuates the field-plate effect on the drain region 38 (i.e.,it worsens the capacity of reducing the electrical field in theproximity of the portion of the drain region 38 that faces the gateelectrode 30), but affords the advantage of a lower output capacitanceas compared to the power device 20 of FIG. 2.

FIG. 5 shows an elementary cell 71 of a power device 70 according to afurther embodiment of the present disclosure. Elements of the elementarycell 71 that are in common with those of the elementary cell 21 of FIG.2 are designated by the same reference numbers and will not be describedany further.

The elementary cell 71 of FIG. 5 further comprises a buffer region 72,having the second conductivity (e.g., of a P type), which extends in thestructural region 26 underneath, and in electrical contact with, thebody region 44. The buffer region 72 is obtained, for example, by meansof an implantation of dopant species. The doping concentration is,according to one aspect of the present disclosure, of around1·10¹⁷-2·10¹⁷ cm⁻³. The extension in the direction X of the bufferregion 72 is equal to or smaller than the extension, once again along X,of the body region 44. The presence of the buffer region 72 enablesreduction of the short-channel effects (SCEs), such as, for example, thedecrease in threshold voltage and punch-through, and moreover improvesthe effectiveness of the superjunction.

FIG. 6 shows an elementary cell 81 of a power device 80 according to anembodiment alternative to that of FIG. 5. Elements of the elementarycell 81 that are in common with those of the embodiments of FIGS. 2-5are designated by the same reference numbers and are not described anyfurther. In this case, a buffer region 82 is obtained by epitaxialgrowth of a buffer layer having the second conductivity (e.g., of a Ptype) and doping concentration, for example, of around 1·10¹⁶-1·10¹⁷cm⁻³. The elementary cell 81 hence comprises the structural region 26,which extends over the substrate 22, and the buffer region 82, whichextends over the structural region 26. The body region 44, the sourceregion 46, and the enriched region 48 extend in the buffer region 82.The structural region 26 and the buffer region 82 form together astructural layer 84. Also in this case, the presence of the bufferregion 82 enables reduction of the short-channel effects and improvesthe effectiveness of the superjunction.

FIG. 7 shows an elementary cell 91 of a power device 90 according to afurther embodiment. Elements of the elementary cell 91 that are incommon with those of the embodiments of FIGS. 2-6 are designated by thesame reference numbers and are not described any further. In this case,the structural region 26 has the second conductivity (e.g., of a Ptype), with a doping concentration of around 5·10¹⁵-2·10¹⁶ cm⁻³. In thisembodiment it is hence the structural region 26 itself that has also thefunction of buffer region, in a way similar to what has been describedwith reference to FIGS. 5 and 6. The elementary cell 91 of FIG. 7moreover has a first trench conductive region 32′ similar to the firsttrench conductive region 32′ of FIG. 4. The first trench conductiveregion 32′ hence extends in the structural region 26, in the directionZ, until it reaches a depth smaller than the thickness, measured along Zstarting from the first side 26 a, of the structural region 26. Thefirst trench conductive region 32′ is electrically insulated from thestructural region 26 by the first and second trench dielectrics 34, 36.According to the embodiment of FIG. 7, use of a structural region 26,having a more concentrated doping as compared to the P− concentration ofthe region 26 of FIGS. 2-6, enables a superjunction to be obtained evenin the presence of the first trench conductive region 32′ that isshallower (i.e., in use, even in the presence of an electrode atreference voltage GND, e.g., ground voltage, which does not extendthroughout the thickness of the structural region 26 and of the drainregion 38).

FIG. 8 shows an elementary cell 101 of a power device 100 according to afurther embodiment. The elementary cell 101 is similar to the elementarycell 91, and elements that are in common therewith are designated by thesame reference numbers and are not described any further. In particular,as described with reference to FIG. 7, the structural region 26 has thesecond conductivity (e.g., of a P type), and a doping concentration ofaround 2·10¹⁶-5·10¹⁶ cm⁻³. The elementary cell 101 moreover has a bufferlayer 102 having the first conductivity (e.g., of an N type), whichextends between the substrate 22 and the structural region 26. Inparticular, the buffer layer 102 extends in direct contact with thefirst side 22 a of the substrate 22. The structural region 26 and thebuffer layer 102 form a structural layer 104.

The buffer layer 102 is indifferently obtained by epitaxial growth orimplantation of dopant species which have the first conductivity. Thedoping concentration of the buffer layer 102 is of around 5·10¹⁵-5·10¹⁶cm⁻³. The thickness of the buffer layer 102 is, for example, comprisedbetween 0.4 μm and 0.8 μm. The presence of the buffer layer 102 enablesimprovement (i.e., increase) of the value of the breakdown voltage ofthe power device 100.

The embodiments of FIGS. 4-8 also enable use of thin gate oxides(dielectric layer 28) (in the region of 30-40 nm), and dimensions ofwidth W of the gate electrode 30 in the range 0.3 μm-0.4 μm, so as toreduce the value of input capacitance of the respective power device.

According to the embodiments of FIGS. 2-8, the vertical drain region 38(having a main extension along Z) enables minimization of the pitch ofthe power device thus obtained. At the same time, the benefits alreadydescribed with reference to the field plate, to the superjunction, andto the reduction of the capacitances inside the power device areobtained.

Irrespective of the particular embodiment, the power device according tothe present disclosure presents the following advantages: the phenomenaof hot-carrier injection (HCl) are negligible thanks to theimplementation of a superjunction; the specific on-state resistanceR_(DS) _(—) _(ON) has an optimized value thanks to the reduction in thevalue of pitch of the elementary cell and to the lateral-doping doses(LDD) used; low gate charge Q_(G) (parasitic capacitances inside thedevice of low value); moreover, high versatility due to integration of amonolithic half-bridge, thanks to the drain terminal on the back.

With reference to FIGS. 9-24 manufacturing steps for producing a powerdevice 110 are now described. The power device 110 comprises twoelementary cells 21 of the type shown in FIG. 2 (modifications that areevident to the person skilled in the branch likewise enable elementarycells to be obtained according to the embodiments of FIGS. 3-8). Themanufacturing steps described hereinafter may be used indifferently toproduce a power device including a single cell or a plurality ofelementary cells, equal to, or higher than, two.

With reference to FIG. 9, a wafer 200 is provided, including thesubstrate 22, made of semiconductor material, for example silicon,having the first conductivity, in this case of an N type, and dopinghigher than 1·10¹⁹ cm⁻³.

The substrate has the first side 22 a and the second side 22 b oppositeto one another and substantially orthogonal to the direction Z. Formedon the first side 22 a is the structural region 26, for example byepitaxial growth of silicon. The structural region 26 has, according toone embodiment, the second conductivity with a doping concentration ofapproximately 1·10¹⁵ cm⁻³.

According to a different embodiment, the structural region 26 has thefirst conductivity with a doping concentration of approximately 1·10¹⁵cm⁻³. Doping of the structural region 26 is obtained by introducingappropriate dopant species in the reaction chamber during the epitaxialgrowth. Alternatively, doping of the structural region 26 is obtained byimplantation of dopant species at the end of, or during, formation ofthe structural region 26. For example, a doping of an N type is obtainedwith arsenic or phosphorus, whereas a doping of a P type is obtainedwith boron.

Then, the dielectric layer 28 is formed, made, for example, of siliconoxide SiO₂. The dielectric layer 28 is formed, for example, by thermaloxidation of the structural region 26, or by deposition of dielectricmaterial. The dielectric layer 28 has a thickness of between 30 nm and60 nm.

The process then proceeds with formation of the stack of layers, which,in subsequent manufacturing steps, form one or more gate electrodes 30.For this purpose, formed by deposition on the dielectric layer 28 is afirst intermediate layer 30 a of doped polysilicon, in particular of anN type, having a thickness comprised between 300 nm and 400 nm. Then,formed on the first intermediate layer 30 a is a second intermediatelayer 30 b, made, for example, of silicide (formed in a way in itselfknown, with a process of thermal reaction) or of deposited metal. Thesecond intermediate layer 30 b has a thickness comprised between 100 nmand 200 nm. The first intermediate layer 30 a is the gate electrodeproper, whereas the layer 30 b has the function of metal electrode.

Next, formed on the second intermediate layer 30 b is a thirdintermediate layer 30 c, made of dielectric material, for example bydeposition of silicon oxide SiO₂. The third intermediate layer 30 c has,for example, a thickness comprised between 300 nm and 400 nm.

Then, formed on the third intermediate layer 30 c is a fourthintermediate layer 30 d, made, for example, of deposited siliconnitride. The fourth intermediate layer 30 d has, for example, athickness of between 70 nm and 140 nm, and has the function of etch-stoplayer in the steps of etching of the insulating layer 36 (see the stepof FIG. 22).

Next, gate electrodes 30 are defined, via masked etching. With referenceto FIG. 10, formed on the wafer 200 is a photoresist mask 112, designedto protect regions of the wafer 200 in areas corresponding to which gateelectrodes 30 are to be formed. One or more etches are then carried out(represented, by way of example, by arrows 114 in FIG. 10) for removingselectively the fourth, third, second, and first intermediate layers 30d-30 a in areas corresponding to regions of the wafer 200 not protectedby the mask 112. The etches of FIG. 10 include etches of a dry type withetching chemistries that are chosen according to the need and thattypically vary according to the layer to be etched.

Then (FIG. 11), the mask 112 is removed from the wafer 200 to obtaingate electrodes 30 (two gate electrodes 30 are represented in FIG. 11).The gate electrodes 30 are separated from one another by a distance d₁,measured in the direction X, comprised between approximately 0.6 μm andapproximately 0.8 μm.

Next (FIG. 12), the body region 44 is formed. For this purpose, formedon the wafer 200 is a mask 116, made, for example, of photoresistdesigned to protect the wafer 200 except for regions of the lattercomprised between gate electrodes 30 facing one another in the directionX. A step of implantation of dopant species which have the secondconductivity (for example, boron) is then carried out, as represented bythe arrows 118 in FIG. 12. The implantation is carried out with animplantation energy of approximately 30-50 keV, which can in any case bemodulated on the basis of the thickness of the dielectric layer 28 andof the desired implantation depth. An implanted region 43 is thusformed, in the structural region 26, having a lateral extension (alongX) substantially equal to the distance d₁ (once again measured along X)between the side walls 30′ that belong to different gate electrodes 30,directly facing one another.

Then (FIG. 13), a step of thermal annealing, at a temperature of between1000° C. and 1100° C. for a time of approximately 20-40 minutes, enablesdiffusion of the implanted region 43 to form the body region 44. Thebody region 44 extends, in top plan view, between the gate electrodes 30and underneath the gate electrodes 30.

Next (FIG. 14), formed on the wafer 200 is a photoresist mask 122,having an extension similar to that of the mask 116 of FIG. 12. The mask122 covers the wafer 200 except for the regions of the latter comprisedbetween walls 30′ of respective gate electrodes 30 directly facing oneanother in order to form source regions. Then an implantation(represented by arrows 124) of dopant species (for example, arsenic orphosphorus), which have the first conductivity (N), is carried out withimplantation energy of approximately 60-140 keV, to form an intermediatesource region 46′ facing the first side 26 a of the structural region 26and completely surrounded, on the remaining sides, by the body region44.

Then (FIG. 15), using the same mask 122, a further implantation ofdopant species (for example, boron) which have the second conductivity(P) is carried out with implantation energy of approximately 180-240keV, and with implantation dose of approximately 1·10¹⁴ cm⁻². Said stepis represented in FIG. 15 by arrows 126. An implanted region is thusformed that provides the enrichment region 48.

In alternative embodiments, the enrichment region 48 can be obtainedwith implantation carried out after formation of the spacers 40 a and 40b.

The implantation energy chosen during the step of FIG. 15 is such as toobtain an implanted region 48 inside the body region 44 but extending toa depth greater than the depth of the intermediate source region 46′ insuch a way that the implanted region 48 is separated from the top side26 a of the structural region 26 by the intermediate source region 46′.

Then (FIG. 16), a step of deposition of dielectric material is carriedout, for example, using the LPCVD or PECVD technique, on the wafer 200,for example silicon oxide SiO₂, having a thickness of between 100 nm and500 nm, in particular between 100 and 200 nm. A covering dielectriclayer 128 is thus formed, which covers the gate electrodes 30 and thedielectric layer 28. Next (FIG. 17), the covering dielectric layer 128is etched with anisotropic dry etching, for example using a dry etchwith etching chemistry CF₄/CHF₃/Ar (HDP plasma) or else C₂F₆/CHF₃/He(RIE plasma).

Said etching step is carried out so as to remove completely the coveringdielectric layer 128 from the wafer 200 except for portions of thecovering dielectric layer 128 adjacent to the side walls 30′ of the gateelectrodes 30.

Moreover, said etching step is continued until portions of thedielectric layer 28 which extend underneath the covering dielectriclayer 128 are removed. The anisotropic dry etch is such that thecovering dielectric layer 128 is removed at a higher rate in areascorresponding to portions of the latter orthogonal to the etchingdirection, whereas portions of the covering dielectric layer 128substantially longitudinal to the etching direction (for example, theportions of the covering dielectric layer 128 that extend along the sidewalls 30′ of the gate electrodes 30) are removed at a lower rate. Alongthe side walls 30′ of the gate electrodes 30, spacers 40 a and 40 b arethus formed, which have a substantially triangular shape, or a shapetapered along Z such that the lateral thickness, measured along X, ofthe spacers 40 a, 40 b, decreases starting from the top side 26 a of thestructural region 26. In particular, the spacers 40 a, 40 b have a baseside having a thickness, measured along X, equal to approximately thethickness chosen for the covering dielectric layer 128 (e.g., between100 and 200 nm).

Moreover, the spacers 40 a, 40 b protect, during the previous etchingstep, portions of the dielectric layer 28 that extend underneath them,which are thus not removed.

Then (FIG. 18), deep trenches 132 are formed, which extend completelythrough the structural region 26 and through part of the substrate 22alongside the gate electrodes 30 (in particular, at the side of the gateelectrodes that does not border on the intermediate source region 46′).

The trenches 132 are formed by anisotropic etching of the structuralregion 26 and of the substrate 22. According to one embodiment, anetching of a DRIE type is used.

In order to protect the intermediate source region 46′ from the etch, aphotoresist mask 133 is formed in an area corresponding to theintermediate source region 46′, between the gate electrodes 30. Withreference to FIG. 18, the spacer 40 a adjacent to the gate electrode 30on the left, and the spacer 40 b adjacent to the gate electrode 30 onthe right function as further alignment masks for the trenches 132, suchthat the trenches 132 have a respective portion of the respective innerwall 132′ vertically aligned (along Z) with the respective spacers 40 a,40 b.

Then (FIG. 19), the mask 133 is removed, and the wafer 200 is subjectedto RTO (rapid thermal oxidation) at a temperature of approximately 1000°C. for 30-60 s, in order to grow thermally an oxide layer on thenon-protected portions of the wafer 200. In this way, thetrench-dielectric layer 3 (or trench-oxide layer), having the functionof pre-implantation oxide, is formed in regions corresponding to therespective inner walls 132′ of the trenches 132. Moreover, since alsothe first side 26 a of the structural region 26 that the intermediatesource region 46′ faces is exposed, a thermal-oxide layer is formed onthe intermediate source region 46′.

Then (FIG. 20), a step of implantation of dopant species having thefirst conductivity (N) is carried out to form drain regions 38. Theimplantation is represented schematically in FIG. 20 by arrows 139 and140.

The step of implantation of FIG. 20 comprises an implantation of dopantspecies of an N type (e.g., phosphorus or arsenic), with implantationenergy comprised between 100 keV and 300 keV, implantation angle α_(I)comprised between −15° and −10° (measured with respect to the directionZ), and implantation doses of a value comprised between approximately1·10¹³ cm⁻² and approximately 5·10¹³ cm⁻². An implanted region is thusobtained, which, in subsequent manufacturing steps, forms the drainregion 38 illustrated on the left of the portion of device of FIG. 20.Likewise, by carrying out an implantation of dopant species of an N typewith implantation angle β_(I) comprised between +10° and +15° (measuredwith respect to the direction Z) and implantation doses ranging betweenapproximately 1·10¹³ cm⁻² and approximately 5·10¹³ cm⁻², an implantedregion is obtained, which, in subsequent manufacturing steps, forms thedrain region 38 illustrated on the right of the portion of device ofFIG. 20.

Then, a step of thermal annealing is carried out to favor diffusion ofthe implanted dopant species (e.g., at 1000° C. for 30 s). In this step,there is also the diffusion of the dopant species implanted in theprevious steps (e.g., during the steps of FIGS. 14 and 15). The drainregions 38 are thus obtained, which have, according to a non-limitingembodiment, a level of doping ranging between approximately 1·10¹⁷ cm⁻³and approximately 6·10¹⁷ cm⁻³.

Then (FIG. 21), the trenches 132 are partially filled with a furtherdielectric layer, which provides the second trench dielectric 36. Thesecond trench dielectric 36 is formed by means of a step of depositionof dielectric material, for example, silicon oxide or silicon nitride,on the wafer 200. A subsequent masked-etching step, shown in FIG. 22,enables removal of the non-desired dielectric layer from the wafer 200except for the areas protected by a mask 145. The mask 145, made, forexample, of photoresist, is formed in areas corresponding to thetrenches 132 and protects the wafer 200 except for the surface portionof the latter that extends between adjacent gate electrodes 30, i.e.,over the intermediate source region 46′. The step of etching of thewafer 200 continues for removal of the dielectric layer 28′ that extendsover the intermediate source region 46′ between the gate electrodes 30,and for removal of a portion of the structural region 26 to form atrench 152. The trench 152 extends through the intermediate sourceregion 46′ and terminates inside the enriched region 48. The trench 152defines two source regions 46. In other words, the source regions 46 areseparated from one another by the trench 152.

With reference to FIG. 23, the trenches 132 and the trench 152 arefilled with conductive material, for example metal such as aluminum ortungsten. First trench conductive regions 32 are thus provided in thetrenches 132 and the second trench conductive region 52 is provided inthe trench 152. Then, with reference to FIG. 24, the sourcemetallization 56 is formed by depositing conductive material, inparticular metal, on the wafer 200, in particular in electrical contactwith the first trench conductive regions 32 and the second trenchconductive region 52. Moreover, a further step of deposition ofconductive material, in particular metal, on the back of the wafer 200(at the second side 22 b of the substrate 22) enables formation of thedrain metallization 41.

The embodiment of FIG. 5, in which the buffer region 72 is present, maybe obtained by inserting a further step of implantation of dopantspecies that have the second conductivity prior to the step ofimplantation of the region 43 of FIG. 12 or, as an alternative,following upon the step of implantation of the region 43 of FIG. 12, or,again alternatively, after the step of thermal annealing to favordiffusion of the region 43 in order to form the body region 44. Theimplantation for the formation of the buffer region 72 is carried outusing an implantation energy higher than the one used for theimplantation of the region 43 of FIG. 12 so as to reach a greater depthin the structural region 26.

The embodiments of FIGS. 7 and 8, in which filling regions 64 arepresent, which extend on the bottom of the trenches 132, may be obtainedby causing the step of FIG. 23 (deposition of conductive material forfilling the trenches 132, 152) to be preceded by one or more steps ofdeposition of dielectric material, for example silicon nitride andsilicon oxide, inside the trenches 132. According to this embodiment,shown in FIG. 25, the filling region 64 includes two filling subregions64 a and 64 b of respective dielectric materials that can be etchedselectively. For example, the dielectric subregion 64 a is made ofsilicon nitride, and the dielectric subregion 64 b is made of siliconoxide.

According to this embodiment, after deposition of the second trenchdielectric, formed on the wafer 200 is a silicon-nitride layer having athickness of some tens of nanometers. The silicon-nitride layer isformed by deposition of Si₃N₄, which penetrates in the trenches 132 toform a silicon-nitride layer on the walls and on the bottom of thetrenches 132 (i.e., forming the filling subregion 64 a). Then, formed onthe wafer 200 is a silicon-oxide layer having a thickness of somehundreds of nanometers (e.g., 200 nm), which fills, at least partially,the trenches 132. Then, by etching selectively the silicon oxide with anetching chemistry having a high selectivity in regard to siliconnitride, the silicon oxide is removed partially inside of the trenches132 to form the dielectric subregion 64 b, which fills part of thetrenches 132 (in particular, the bottom of the trenches 132). Bymodulating appropriately, and in a way in itself known, the duration ofthe etch, it is possible to remove the desired amount of silicon oxidefrom the trenches 132. The latter etch is moreover designed to removethe oxide layer deposited on the wafer 200 outside the trenches 132,until the underlying silicon-nitride layer (deriving from theimmediately previous deposition step) is reached. Finally, saidsilicon-nitride layer may be removed from the wafer 200 with an etch ofa standard type, without the need to resort to any photomask. Inside thetrenches 132, the silicon-nitride layer is removed elsewhere, except forthe areas of the latter protected by the dielectric subregion 64 b. Asecond filling region 64 is thus formed, comprising the dielectricsubregion 64 a, made of silicon nitride, which surrounds laterally andat the bottom the dielectric subregion 64 b, made of silicon oxide. Itis thus possible to proceed with formation of the first trenchconductive region 32′, in the way already described previously. It isevident that the dielectric subregions 64 a and 64 b may be made ofdielectric materials different from those indicated by way of example.

According to a further embodiment (not shown in the figure), the fillingregions 64 are provided by causing the step of formation of the secondtrench dielectric 36 to be followed by a step of formation (e.g.,deposition) of a third trench dielectric having an etching rate higherthan the respective etching rate of the second trench dielectric 36. Inthis way, it is possible to modulate etching of the third dielectricwithout incurring in undesirable damage to the second trench dielectric36. The third dielectric may, for example, be etched in such a way as toremove it only in part from the trenches 132 but completely from therest of the wafer. The trenches 132 are thus partially filled withdielectric material in areas corresponding to their bottom.

FIG. 26 shows a further embodiment of an elementary cell 171 of a powerdevice 170. According to FIG. 26, in each trench 132 a trench dielectric136 is present, which surrounds the first trench conductive region 32.The trench dielectric 136, as better illustrated in FIGS. 27 a-27 ecomprises a plurality of dielectric layers set on top of one another.The trench dielectric 136 has a thickness, measured in the direction Xstarting from the wall 132′ of the respective trench 132, which varieswhen measured at different depths (along Z). In particular, saidthickness has a minimum value d_(MIN) when measured substantially at thefirst side 26 a of the structural region 26 and as far as the depth z₁,and a maximum value d_(MAX) at a greater depth, until the bottom end ofthe first trench conductive region 32 is reached.

Even more in particular, the thickness (along X) of the trenchdielectric 136 is equal to d_(MIN) substantially as far as a depth z₁,measured starting from the first side 26 a of the structural region 26,approximately equal to the depth reached by the body region 44. Then,beyond a depth z₁ in the trench 136, the thickness (along X) of thetrench dielectric 136 passes, as has been said, to the maximum valued_(MAX). According to this embodiment, d_(MIN) is given by the sum ofthe thicknesses, along X, of the trench-oxide layers 34 and 36, andd_(MAX) is given by the sum of the thicknesses, along X, of thetrench-oxide layers 34 and 36, and thicknesses, along X, of the layers181 and 183 (the latter are shown hereinafter in FIG. 27 e, anddescribed with reference to said figure).

Consequently, the conformation of the first trench conductive regions 32follows the conformation of the trench dielectric 136. The first trenchconductive regions 32, hence, have a thickness, in cross-sectional viewand along X that is maximum when measured at the first side 26 a of thestructural region 26, and minimum when measured at the bottom end of thefirst trench conductive region 32.

Steps of formation of the trench dielectric 136, having the conformationrepresented in FIG. 26, are shown in FIGS. 27 a-27 e. In particular,FIGS. 27 a-27 e show, in cross-sectional view, an enlarged detail ofFIG. 26, at the trench 132 filled with the trench dielectric 136.

With reference to FIG. 27 a (here only one trench is shown but what hasbeen described equally applies to a plurality of trenches), after thestep of FIG. 21, deposited on the wafer 200 (and hence also in thetrench 132) are successive layers of silicon nitride 181, silicon oxide183, and polysilicon 185. The second trench dielectric 36, formedaccording to the step of FIG. 21, has, according to this embodiment, athickness equal to d_(MIN) comprised between 50 nm and 200 nm. Thesilicon-nitride layer 181 has a thickness of some tens of nanometers,and the silicon-oxide layer 183 has a thickness of approximately 100 nm.The polysilicon layer 185 is deposited until the trench 132 is filledcompletely.

Then (FIG. 27 b), a partial etch of the polysilicon layer 185 is carriedout (etch selective with respect to the silicon oxide) in such a way asto remove the polysilicon 185 until the depth equal to approximately z₁is reached. Consequently, following upon this step, the bottom of thetrench 132 is filled completely with respective portions of the layersof silicon nitride 181, silicon oxide 183, and the remaining polysilicon185 not removed by the etch.

Then (FIG. 27 c), an etch of the silicon oxide 183 is carried out so asto remove completely said layer from the wafer 200 and from the trench132 except for the portion of the silicon-oxide layer 183 protected bythe polysilicon 185 not removed at the previous step of FIG. 27 b. Then(FIG. 27 d), the silicon-nitride layer 181 is removed from the wafer 200and from the trench 132 except for the portion of the silicon-nitridelayer 181 protected by the silicon oxide 183 and by the polysilicon 185not removed in the steps of FIGS. 27 b and 27 c.

Next (FIG. 27 e), the polysilicon 185 is removed completely from thetrench 132. A further dielectric layer is thus formed in depth in thetrench 132, in particular starting substantially from the depth z₁ asfar as the bottom of the trench 132. This further dielectric layer has athickness equal to d_(MAX)−d_(MIN) and, together with the second trenchdielectric 36, forms the trench dielectric 136 of FIG. 26. Processing ofthe wafer 200 can then proceed with the steps of FIG. 23 onwards.

This embodiment presents the advantage of improving the degree offreedom between the on-state drain-to-source resistance R_(DS) _(—)_(ON) and the phenomenon of hot-carrier injection (HCl). Theconformation of the dielectric region 36 of FIG. 26 presents theadvantage of enabling a ground shield to be obtained that is closer tothe drain region 38 in the proximity of the gate electrode 30 (which isa critical region for the HCl phenomenon), with consequent reduction ofthe electrical field and hence of the carrier-trapping phenomenon.Descending in depth along Z, the thickening of the dielectric 136 (fromthe value d_(MIN) to the value d_(MAX)) prevents accumulation of thelines of potential on the terminal part of the shield up against thedrain region 38, with consequent reduction of the electrical field insaid region.

Moreover, the potential lines resulting from a structure of this typehave a smooth curvature in so far as, as has been said, a thickdielectric 136 (with a thickness d_(MAX)) makes it possible to renderthe lines of field in said region less dense. Hence, the distribution ofelectrical field is improved as compared to devices of a known type andalso as compared to the embodiments of FIGS. 4, 7, 8.

FIG. 28 a shows a circuit diagram of a half-bridge block provided bymeans of two MOSFETs. FIG. 28 b shows, in cross-sectional view, a wafer300 including a monolithic block of MOSFETs that provide the half-bridgeblock of FIG. 28 a.

With reference to FIG. 28 a, a first transistor T1 of an N type, and asecond transistor T2, which is also of an N type, are present, whichhave each a respective drain electrode D, source electrode S, and gateelectrode G.

The drain electrode D of the transistor T1 (“high-side” transistor) canbe biased, in use, at a voltage V_(H), whilst the source electrode S ofthe transistor T2 (“low-side” transistor) can be biased, in use, at avoltage V_(L), with V_(H)>V_(L). The source electrode of the transistorT1 is electrically coupled to the drain electrode of the transistor T2at a common node 310.

With reference to FIG. 28 b, the transistor T1 is set on the left of thesection shown, whereas the transistor T2 is set on the right of thesection shown.

The wafer 300 comprises a substrate 301, made of semiconductor material,for example silicon, with a doping of an N+ type, and a structuralregion 302, for example silicon grown epitaxially, of a P type. Thestructural region 302 has a top side 302 a and a bottom side 302 b,where the bottom side 302 b is in contact with the substrate 301.

The transistor T1 includes: gate electrodes 315 arranged on the top side302 a of the structural region 302 and separated from the latter by agate dielectric layer 303; body regions 316, formed in the structuralregion 302 and facing the top side 302 a of the structural region 302;source regions 318 formed in the structural region 302, inside the bodyregions 316, and facing the top side 302 a of the structural region 302;p-wells 319 formed in the structural region 302, inside the body regions316, underneath the source regions 318; and drain regions 320, whichextend in the structural region 302, facing the top side 302 a of thestructural region 302, between body regions 316. One or more plugs 322made of electrically conductive material, for example metal, extendthrough the structural region 302 starting from the top side 302 a untilthe substrate 301 is reached, and terminating inside the substrate 301.The plugs 322 are in electrical contact with respective source regions318 and have the function of forming an electrical connection betweenthe source regions 318 and the substrate 301.

Extending over the structural region 302 and the gate electrodes 315 isa dielectric layer 326, for example made of silicon oxide, as aprotection and insulation of the gate electrodes and of the plugs 322. Afurther conductive plug 324 extends through the dielectric layer 326 andthe gate oxide 303 until it reaches and comes into electrical contactwith the drain region 320. In order to favor said electrical contact,the drain region 320 locally has an electrical-contact region 328 havinga level of doping higher than the doping of the drain region 320.

A metallization 330 extends over the wafer 300, on the dielectric layer326, in electrical contact with the plug 324, to form a drain electrodeD of the transistor T1. A metallization 332 extends over the back of thewafer 300, in electrical contact with the substrate 301 and with thesource regions 318 (via the substrate 301 and the plugs 322). Themetallization 332 concurs in forming a source electrode for thetransistor T1.

The transistor T2 is a power device according to any one of theembodiments described with reference to FIGS. 2-8 or to FIGS. 26 and 29,and obtained according to the manufacturing steps described previously.

The transistor T2 includes: gate electrodes 335 arranged on the top side302 a of the structural region 302 and separated from the latter by thegate dielectric layer 303; body regions 336, formed in the structuralregion 302 and facing the top side 302 a of the structural region 302;source regions 338 formed in the structural region 302, inside the bodyregions 336, and facing the top side 302 a of the structural region 302;p-wells 339 formed in the structural region 302, inside the body regions336, underneath the source regions 338; and drain regions 340 (LDDregions), which extend vertically in the structural region 302 (in thedirection Z), between the top side 302 a of the structural region 302and the bottom side 302 b of the structural region 302.

A conductive plug 341 extends through the dielectric layer 326 and thegate oxide 303 until it reaches and comes into electrical contact withrespective source regions 338 and p-wells 339. A metallization 342extends over the wafer 300, on the dielectric layer 326, in electricalcontact with the plug 341, to form a source electrode S of thetransistor T2. The metallizations 330 of the transistor T1 and 342 ofthe transistor T2 are electrically insulated from one another.

The transistor T2 further comprises deep trenches 346, which extendthrough the dielectric layer 326, the gate oxide 303, the structuralregion 302, and part of the substrate 301, to terminate in the substrate301. In particular, the trenches 346 are, in this case, providedaccording to the embodiment of FIG. 29 (definition and etching using thelithographic technique), but can alternatively be provided according toany of the embodiments described with reference to FIGS. 2-8 or FIG. 26,and manufactured as described with reference, in particular, to FIGS.18-23.

The trenches 346 include one or more dielectric insulation layers 348and an internal conductive region 349, surrounded by the one or moredielectric insulation layers. In particular, the trenches 346 extendadjacent to the drain regions 340.

The drain regions 340 of the transistor T2 are in electrical contactwith the substrate 301 and with the metallization 332. Consequently, thesource regions 318 of the transistor T1 and the drain regions 340 of thetransistor T2 are electrically coupled together. The metallization 332and the substrate 301 provide the common node 310 of FIG. 28 a.

From an examination of the characteristics of the disclosure providedaccording to the present disclosure, the advantages that it affords areevident.

The horizontal dimensions (measured along X), or pitch, of a powerdevice according to any one of the embodiments of the present disclosureare considerably reduced as compared to the known art; the drainelectrode is provided on the back of the wafer, enabling a packaging ofa standard type; the performance is not impaired, and is comparable tothat of horizontal-channel LDMOS devices of a known type.

Moreover, thanks to the fact that during formation of the LDD regionsthe spacers 40 a, 40 b function as hard-masks, the alignment between thegate electrodes and the drain regions is carefully controlled, reducingthe parasitic capacitances.

Thanks to the implementation of the concept of superjunction, thephenomena of hot carrier injection are negligible.

The specific on-state drain-to-source resistance R_(DS) _(—) _(ON) islow thanks to the reduced pitch of the elementary cell (and hence of adevice including a plurality of elementary cells) and thanks also to thedoses of LDD used.

In addition, the internal capacitances are minimized, enabling reductionof the gate charge Q_(G).

Finally, it is clear that modifications and variations may be made towhat has been described and illustrated herein, without therebydeparting from the sphere of protection of the present disclosure.

For example, as shown in FIG. 29, the steps of FIGS. 16 and 17, whichlead to formation of the spacers 40 a and 40 b, may be replaced by astep of formation of a thick dielectric layer 420, for example siliconoxide deposited, on gate electrodes 30, so as to cover the gateelectrodes 30 completely. Then, said thick dielectric layer 420 isselectively removed in regions of the wafer in which the trench/trenches132 and the trench/trenches 152, are to be formed, and is preservedalongside, and above, the gate electrodes 30. In this way, etching ofthe wafer to form the trench/trenches 132 and the trench/trenches 152may be carried out without the aid of further masks in so far as thethick dielectric layer 420 operates itself as etch mask.

Filling of the trenches 132 includes one or more dielectric layers and aconductive filling 32, according to any one of the embodiments of FIGS.1-8, and 26.

According to a further embodiment, shown in FIG. 30, an elementary cell448 of a power device 449 includes trenches 132 completely filled withdielectric material, for example silicon oxide, which forms a trenchfilling dielectric 450. A protective dielectric layer 460, made, forexample, of silicon oxide, moreover covers the gate electrodes 30,which, in this case, include a polysilicon layer 30 a and a silicidelayer 30 b. The protection dielectric layer 460 protects and insulateselectrically the gate electrodes. According to one embodiment, thelayers 450 and 460 are formed simultaneously in a single step ofdeposition of silicon oxide, or other dielectric material. Elements ofthe elementary cell 448 that are in common to those of the elementarycell 21 of FIG. 2 are designated by the same reference numbers and arenot described any further. The alternative embodiments of FIG. 6 (withreference to the presence of the region 82) and of FIG. 8 (withreference to the region 102) may be applied to the embodiment of FIG.30.

The various embodiments described above can be combined to providefurther embodiments. These and other changes can be made to theembodiments in light of the above-detailed description. In general, inthe following claims, the terms used should not be construed to limitthe claims to the specific embodiments disclosed in the specificationand the claims, but should be construed to include all possibleembodiments along with the full scope of equivalents to which suchclaims are entitled. Accordingly, the claims are not limited by thedisclosure.

1. An electronic semiconductor device comprising: a semiconductor bodyhaving a first side and a second side opposite to one another along afirst direction and including a first structural region, which faces thesecond side and has a first conductivity; and a second structural regionwhich extends over the first structural region, faces the first side,and has a second conductivity opposite to the first conductivity; a bodyregion having the second conductivity and extending in the secondstructural region at the first side; a source region having the firstconductivity, extending within the body region and facing the firstside; a drain region having the first conductivity and facing the firstside of the semiconductor body; a gate electrode extending over aportion of the first side of the semiconductor body between the sourceregion and the drain region; a first trench which extends through thesecond structural region and houses a trench dielectric region and afirst trench conductive region; and a second trench which extendsthrough part of the second structural region inside the body region,said second trench housing a second trench conductive region inelectrical contact with the body region and with the source region,wherein the drain region extends through the second structural region,electrically contacts the first structural region, and is arrangedbetween, and in direct contact with, the body region and the trenchdielectric region, said first and second trench conductive regions beingelectrically coupled to one another.
 2. The device according to claim 1,wherein the first trench extends throughout a thickness of the secondstructural region and through part of the first structural region andterminates in the first structural region.
 3. The device according toclaim 1, wherein the trench dielectric region extends on an inner walland on a bottom of the first trench.
 4. The device according to claim 1,wherein the first trench conductive region extends throughout athickness of the second structural region and is electrically insulatedfrom the first and second structural regions by the trench dielectricregion.
 5. The device according to claim 1, wherein the first trenchconductive region extends only for a portion of a thickness of thesecond structural region and is electrically insulated from the firstand second structural regions by the trench dielectric region.
 6. Thedevice according to claim 1, wherein the trench dielectric region has afirst thickness at a first depth value in the semiconductor body and asecond thickness, greater than the first thickness, at a second depthvalue, greater than the first depth value, in the semiconductor body. 7.The device according to claim 6, wherein the trench dielectric regionfurthermore has a third thickness, greater than the second thickness, ata third depth value, greater than the second depth value, in thesemiconductor body.
 8. The device according to claim 1, wherein thedrain region is an implanted region of a light-doped-drain type.
 9. Thedevice according to claim 1, further comprising: a conductive layer thatelectrically couples the first and second trench conductive regions toone another and extends on a top side of the gate electrode; and a gatedielectric layer which extends over the first side of the semiconductorbody between the second structural region and the gate electrode,wherein the gate electrode includes: a conductive gate region in contactwith the gate dielectric layer, and an insulating gate region coveringthe conductive gate region and electrically insulating a top side of theconductive gate region from the conductive layer.
 10. The deviceaccording to claim 1, further comprising an enriched region, which hasthe second conductivity and extends in the body region, said secondtrench conductive region being in electrical contact with the bodyregion via the enriched region.
 11. The device according to claim 1,further comprising a first spacer and a second spacer, which are made ofdielectric material and are arranged on the first side of thesemiconductor body at respective opposite sides of the gate electrode,wherein the second trench conductive region extends alongside the gateelectrode, and is electrically insulated from the gate electrode by thesecond spacer.
 12. A method for manufacturing an electronicsemiconductor device, comprising: defining a first structural regionhaving a first conductivity in a substrate, the first structural regionincluding a first side and a second side; forming, on the first side ofthe first structural region, a second structural region having a firstside exposed and having a second conductivity opposite to the firstconductivity; forming a body region, having the second conductivity, inthe second structural region at the first side of the second structuralregion; forming a source region, having the first conductivity, withinthe body region and facing the first side of the second structuralregion; forming a drain region, having the first conductivity, facingthe first side of the second structural region; and forming a gateelectrode on the first side of the structural region, between the sourceregion and the drain region, removing selective portions of the secondstructural region so as to form a through hole, which extends throughthe second structural region throughout a thickness of the secondstructural region; removing selective portions of the first structuralregion exposed through said through hole so as to form a first trench,which extends through the second structural region; forming a trenchdielectric region inside the first trench; forming a first trenchconductive region inside the trench dielectric region; removingselective portions of the second structural region in the body region soas to form a second trench; forming a second trench conductive regioninside the second trench so that the second trench conductive region isin electrical contact with the body region and with the source region;and electrically coupling together said first and second trenchconductive regions, wherein forming the drain region includes formingthe drain region between, and in direct contact with, the body regionand the trench dielectric region and extending in depth through thesecond structural region coming into electrical contact with, the firststructural region.
 13. The method according to claim 12, wherein thestep of forming the trench dielectric region includes depositing one ormore dielectric materials on an inner wall and on a bottom of the firsttrench.
 14. The method according to claim 12, wherein forming the trenchdielectric region includes: depositing a first layer of fillingdielectric on an inner wall and on a bottom of the first trench; anddepositing a second layer of filling dielectric in the trench, thesecond layer of filling dielectric covering the first layer of fillingdielectric and extending alongside the gate electrode.
 15. The methodaccording to claim 14, wherein forming the trench dielectric regionfurther includes: depositing a third layer of filling dielectric in thefirst trench; removing selectively the third layer of filling dielectricexcept for portions of the third layer of filling dielectric whichextend in regions corresponding to walls of the first trench close tothe bottom of the first trench so that the trench dielectric region hasa first thickness at a first depth value and a second thickness, greaterthan the first thickness, at a second depth value greater than the firstdepth value.
 16. The method according to claim 12, wherein forming thedrain region includes performing a masked slanted implantation of dopantspecies, which have the first conductivity, in the second structuralregion, such that the drain regions extends adjacent to a wall of thefirst trench.
 17. The method according to claim 16, wherein performingsaid masked slanted implantation includes performing said masked slantedimplantation at an implantation angle between ±10° and ±15° with respectto a direction of main extension of the first trench, said implantationhaving an implantation dose ranging from approximately 1·10¹³ cm⁻² toapproximately 5·10¹³ cm⁻².
 18. The method according to claim 16, whereinforming the drain region further includes performing a thermal annealingthat diffuses the dopant species and forms the drain region as alight-doped-drain region.
 19. The method according to claim 12, furthercomprising forming a gate dielectric layer on the first side of thesecond structural region, between the second structural region and thegate electrode, wherein forming the gate electrode includes the substepsof: forming a conductive gate region on the gate dielectric layer, andforming an insulating gate region on the conductive gate region so as toelectrically insulate the conductive gate region.
 20. The methodaccording to claim 12, further comprising forming an enriched region,having the second conductivity, in the body region, wherein forming saidsecond trench conductive region comprising forming said second trenchconductive region in electrical contact with the enriched region. 21.The method according to claim 20, further comprising forming a firstspacer and a second spacer, made of dielectric material, on the firstside of the second structural region, at respective opposite sides ofthe gate electrode, wherein forming the second trench conductive regioncomprises forming the second trench conductive region alongside the gateelectrode, electrically insulated from the gate electrode by the secondspacer.
 22. An electronic semiconductor device comprising: a bridge offirst and second transistors in a semiconductor body having a first sideand a second side opposite to one another along a first direction andincluding a first structural region that faces the second side and has afirst conductivity, wherein the first transistor includes: a secondstructural region which extends over the first structural region, facesthe first side, and has a second conductivity opposite to the firstconductivity; a first body region having the second conductivity andextending in the second structural region at the first side; a firstsource region having the first conductivity, extending within the firstbody region and facing the first side; a first drain region having thefirst conductivity and facing the first side of the semiconductor body;a first gate electrode extending over a portion of the first side of thesemiconductor body between the first source region and the first drainregion; a first trench which extends through the second structuralregion and houses a trench dielectric region and a first trenchconductive region; and a second trench which extends through part of thesecond structural region inside the first body region, said secondtrench housing a second trench conductive region in electrical contactwith the first body region and with the first source region, wherein thefirst drain region extends through the second structural region,electrically contacts the first structural region, and is arrangedbetween, and in direct contact with, the first body region and thetrench dielectric region, said first and second trench conductiveregions being electrically coupled to one another.
 23. The deviceaccording to claim 22, wherein the second transistor includes: a thirdstructural region which extends over the first structural region, facesthe first side, is positioned laterally with respect to the secondstructural region, and has the second conductivity; a second body regionhaving the second conductivity and extending in the third structuralregion at the first side; a second source region having the firstconductivity, extending within the second body region and facing thefirst side; a second drain region having the first conductivity andfacing the first side of the semiconductor body; a second gate electrodeextending over a portion of the first side of the semiconductor bodybetween the second source region and the second drain region; and aconductive via electrically contacting the second source region andextending through the third structural region into electrical contactwith the first structural region.
 24. The device according to claim 22,further comprising a metal layer contacting the second side of thesemiconductor body and extending from at least a position directly belowthe conductive via to at least a position directly below the first drainregion.